The present invention relates to an automatic transmission for a vehicle and, more particularly, an automatic transmission installed longitudinally in the engine room on the basis of the mechanism of the manual transmission.
In case the power unit containing the transmission is arranged longitudinally in the engine room, i.e., in case the power unit is arranged such that the input shaft and the output shaft of the transmission are directed in parallel with the running direction of the vehicle, such power unit is arranged as disclosed in Japanese Patent Application Laid-open No. Hei 7-167257, for example. The power unit disclosed in this Publication is prepared for the four-wheel-drive vehicle. The engine, the clutch housing into which the clutch is incorporated, the transmission main body into which the final reduction gear for driving the front wheel is incorporated, and the transfer unit having the power transfer mechanism of the front and rear wheels are arranged in the engine room in this order from the front side of the vehicle. The power is transmitted from the rear end portion of the transmission to the driving unit that transmits the power to the rear wheel.
The transmission disclosed in this Publication is the manual transmission (MT). The selecting operation of the transmission gear train which transmits the power, out of plural transmission gear trains provided between the input shaft and the output shaft, is executed manually by the operator operating the shift lever. The selecting operation is carried out automatically by the hydraulic actuator in response to the running situation of the vehicle on the basis of the mechanism of such manual transmission. The Automated Manual Transmission (AMT) can be completed as disclosed in Japanese Patent Application Laid-open No. Toku-Kai 2000-65199, for example. In this automatic transmission, the shift clutch, i.e., the bypass clutch is provided to transmit the torque of the input shaft to the output shaft in synchronism with controls of the start clutch and the electronic throttle valve when the transmission gear train is switched by the changeover mechanism that consists of the synchronizer. This bypass clutch is fitted to the gear train at the highest shifting stage. Since the generation of the torque stop during the shifting operation is prevented, the shift shock can be reduced and thus the smooth shifting operation can be carried out.
In this automatic transmission, the bypass clutch is fitted to the highest shifting stage of the parallel two-axle transmission gear train such that the torque of the input shaft is transmitted from the highest shifting stage to the output shaft during the shifting operation. In this case, the bypass clutch consisting of the multiple disc clutch must be provided between the transmission gear train at the highest shifting stage constructed at the rear end portion of the main transmission portion, and the transfer unit from the viewpoint of the space. For this reason, following subjects and disadvantages are caused.
In case the bypass clutch is fitted to the drive train in which the transmission having the transfer unit at its rear end portion and the engine are arranged longitudinally in the engine room, length of the transmission is increased by the thickness dimension of the added bypass clutch. Since the transmission is extended in its axial direction, the rear end portion of the transmission becomes close to tunnel members of the carbody structure and the toe board. Therefore, since the carbody structure is designed with regard to the crash stroke in the crash, the carbody structure must be corrected to reduce the interior space. Also, the expansion of the transmission lowers the flexural rigidity of the transmission itself and thus the vibration and the noise of the drive train become worse. In addition, if either the manual transmission or the automatic transmission is installed into the vehicle having the same carbody structure, there is a possibility that the compatibility of the carbody structure is lost because their outer dimensions of the transmissions are different.
This automatic transmission has the start clutch, the bypass clutch, the oil pump, and the hydraulic control mechanism. It is desired that these elements should be assembled closely by employing the hydraulic circuit that is able to arrange the start clutch and the bypass clutch around the oil pump as close as possible, or reducing the hydraulic circuit extended from the hydraulic control mechanism. However, in the automatic transmission disclosed in Japanese Patent Application-Laid-open No. Toku-kai 2000-65199, there is disclosed such a structure that the start clutch is provided in front of the transmission and also the bypass clutch is provided at the back of the transmission. Thus, the control hydraulic pressure is guided from the hydraulic control mechanism to the hydraulic chambers of respective clutches via the hydraulic circuits. As a result, when respective clutches are controlled by the hydraulic control mechanism arranged normally under the transmission, it is possible to worsen the responsibility because the hydraulic circuits are long. In particular, when the atmospheric temperature is low, such influence is ready to appear. In this manner, the functional disadvantages may be caused in the minute control of the start clutch to attain the smooth start, the momentary control of the hydraulic pressure of the bypass clutch during the shifting operation to get the smooth shifting operation, etc.
It is an object of the present invention to provide an Automated Manual Transmission (AMT) constructed based on the structure of the manual transmission, which is capable of preventing the increase of the transmission in size in the axial direction and also improving the responsibility at the time of hydraulic control.
An automatic transmission of the present invention comprising: an input shaft to which a plurality of driving gears are provided; an output shaft to which a plurality of driven gears are provided, the plurality of driven gears being engaged with the driving gears to constitute a plurality of transmission gear trains respectively; a changeover mechanism for selecting the desired transmission gear train which transmits a power, out of the plurality of transmission gear trains; a start clutch for setting an engine and the input shaft into an engage state and a disengage state; a driving shaft coupled to the output shaft in parallel with the output shaft, the driving shaft being coupled to a final reduction gear; and a bypass clutch arranged over the final reduction gear and transmitting a torque of the input shaft to the output shaft while controlling connection and disconnection in synchronism with a selecting operation of the transmission gear trains in a shifting operation, wherein the manual transmission is arranged longitudinally in an engine room in which the input shaft and the output shaft are arranged in a traveling direction of a vehicle.
In the automatic transmission of the present invention, the bypass clutch comprises a plurality of bypass clutches provided between the input shaft and the output shaft, wherein at least one of the plurality of bypass clutches is arranged over the final reduction gear, and the driving shaft is arranged below the output shaft.
In the automatic transmission of the present invention, the automatic transmission further comprises an oil pump driven by the engine to generate a hydraulic pressure which drives the start clutch and the bypass clutch, wherein the oil pump is arranged over the final reduction gear and near the bypass clutch.
The automatic transmission having the final reduction gear is constructed to have three rotation shafts, and also the bypass clutch is installed over the final reduction gear. Therefore, an upper space of the final reduction gear can be effectively employed, and also the automatic transmission can be shortened in the axial direction.
Since the oil pump can be arranged over the final reduction gear and near the bypass clutch, the upper space of the final reduction gear can be effectively employed and thus the hydraulic pressure source and the hydraulic actuator can be positioned closely. Therefore, the automatic transmission can be shortened in the axial direction and thus the responsibility in the hydraulic pressure control can be improved.